Moving-entity detection

ABSTRACT

Sensing moving entities includes transmitting a stepped-frequency radar signal including multiple frequencies through a wall from a first side of the wall to a second side of the wall. Portions of the radar signal that are reflected by entities located beyond the second side of the wall are detected. The reflected portions are processed to generate processed data including information associated with frequency shifts between the transmitted signal and the detected signal. The processed data is analyzed to determine if reflected portions are associated with moving entities.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a continuation of U.S. application Ser. No.11/428,956, filed Jul. 6, 2006, and titled “Moving-Entity Detection”,which is a continuation of U.S. application Ser. No. 11/279,859, filedApr. 14, 2006, and titled “Moving-Entity Detection”, which claimspriority to U.S. Provisional Application No. 60/671,105, filed Apr. 14,2005, and titled “Wall Penetrating Personnel Detection Sensor (WPPDS)”,all of which are incorporated by reference in their entirety.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

The U.S. Government may have certain rights in this invention asprovided for in the terms under agreement number W15P7T-05-9-P232awarded by DARPA and the US Army Communications-Electronics Command.

TECHNICAL FIELD

This description relates to a detecting moving entities, such asdetecting the presence of a moving person concealed behind a wall in abuilding.

BACKGROUND

Detection sensors may be used to determine the presence of objects whenvisual recognition is difficult.

SUMMARY

In one general aspect, sensing moving entities includes transmitting astepped-frequency radar signal including multiple frequencies through awall from a first side of the wall to a second side of the wall,detecting reflected portions of the radar signal that are reflected byentities located beyond the second side of the wall, processing thereflected portions to generate processed data including informationassociated with frequency shifts between the transmitted signal and thedetected signal, and analyzing the processed data to determine ifreflected portions are associated with moving entities.

Implementations may include one or more of the following features. Forexample, analyzing the processed data may include calibrating theprocessed data, such as by compensating for reflections near or behindthe device. Calibration may be performed for each separate attempt tosense moving entities.

Analyzing the processed data may include removing information associatedwith reflections from stationary objects or from objects within aproximity to the device. Analyzing the processed data also may includeperforming a Fourier transform on information associated with theprocessed data, and degraded performance may be detected based onwhether results of the Fourier transform satisfy a condition. Similarly,a first Fourier transform with a first integration time and a secondFourier transform with a second integration time longer than the firstintegration time may be performed on the same information associatedwith the processed data, and degraded performance may be detected basedon whether results of the first Fourier transform satisfy a firstcondition and results of the second Fourier transform satisfy a secondcondition different from the first condition. Analyzing the processeddata may include analyzing frequency and phase shifts between thetransmitted signal and the detected signal to determine movement ofobjects at a distance.

In another general aspect, a system for sensing moving entities includesa stepped-frequency radar transmitter coupled to a transmit antenna totransmit a stepped-frequency radar signal, a receive antenna configuredto detect reflected portions of the radar signal, and a processoroperable to process, for a multiple frequencies, the reflected portionof the radar signal from the receive antenna and to analyze theprocessed data to determine the presence of moving entities on anopposite side of a wall from a side of the wall on which the system islocated.

Implementations may include one or more of the following features. Forexample, the system may include a demodulator which receives both thestepped-frequency radar signal and a reflected portion of the radarsignal, and outputs in phase and out of phase data. The system may beconfigured to be operable using AA batteries.

The processor may be configured to remove information associated withsignal reflection from stationary objects or from objects within aproximity to the device. The processor also may be configured to performa first Fourier transform with a first integration time and a secondFourier transform with a second integration time longer than the firstintegration time on the same information associated with the processeddata.

The details of one or more implementations are set forth below. Otherfeatures will be apparent from the description and drawings, and fromthe claims.

DESCRIPTION OF DRAWINGS

FIG. 1A is a diagram illustrating a use of a stepped-frequency scannerfor detecting moving entities.

FIG. 1B is a block diagram of a stepped-frequency scanner configured todetect moving entities.

FIGS. 2A and 2B are perspective views of an antenna design for thesystem of FIG. 1B,

FIG. 3 is a diagram of an exemplary conversion system.

FIGS. 4 and 5 are flow charts of processes for detecting movingentities.

FIG. 6 is a flow chart of a process for processing radar signalsreceived by a handheld stepped-frequency scanner.

FIG. 7A is a picture of a handheld stepped-frequency scanner relative toa semi-automatic weapon ammo pouch.

FIG. 7B is a picture of a handheld stepped-frequency scanner in a case.

FIG. 8A is a picture illustrating battery access in a handheldstepped-frequency scanner.

FIG. 8B is a graph illustrating power discharge characteristics in ahandheld stepped-frequency scanner.

FIG. 9A is a picture illustrating recessed light emitting diodes in ahandheld stepped-frequency scanner.

FIG. 9B is a picture illustrating operational controls of a handheldstepped-frequency scanner.

Like reference symbols in the various drawings indicate like elements.

DETAILED DESCRIPTION

In order to detect the presence of entities through movement when visualdetection is blocked (e.g., by a wall), a device, such as a handheldscanner, includes a stepped-frequency radar transmitter. The transmitteremits a radar based signal that includes different frequencies. Theemitted signal strikes objects and is partially reflected. The reflectedsignal may be affected by environmental characteristics (e.g., movementof an object or entity or distance to the object or entity). Forexample, if an object is moving closer to the device, signals reflectedfrom the object will exhibit a frequency shift (i.e., a Doppler shift)that may be observed and processed by the device. Also, the distance asignal travels before being partially reflected affects the phase of thereflected signal at the receiver. The processing methodology used by thedevice determines when the reflected signal appears to result frommovement of an object or entity at a distance.

Detecting differing rates of movements may require separate processingalgorithms and/or separate characteristics of the transmitted signal.For example, in one implementation, a shorter duration (e.g., a fewseconds) of signal transmission at a set of frequencies may betransmitted to detect fast moving objects, such as an individualrunning. A longer duration (e.g., less than 10 seconds) signaltransmission may be employed to detect slower moving objects, such asthe chest cavity of an individual breathing.

The device may be used to aid in military or search and rescue missions.For example, soldiers may use the device to detect the presence ofunknown individuals that may be hiding behind walls. A soldier mayactivate the device while aiming the transmitter such that the signal ispointed at a closed door. The signal may penetrate walls and doors, andpartially reflect when striking an individual (e.g., an enemy soldier).If the individual is moving, the reflected portion of the signal mayexhibit a frequency shift detectable by the device. The device receivesand processes the reflected signal, and may determine the presence ofone or more entities. Also, the device may be used to detect thepresence of individuals buried in piles of rubble based on movement suchas breathing.

FIG. 1A shows an example use 100 of a stepped-frequency sensor deviceconfigured to detect moving entities. A user 105 holds an activatedhandheld stepped-frequency sensor device 110, which transmitsstepped-frequency radar signals. Although multiple signals aretransmitted by the stepped-frequency sensor device, a single transmittedsignal is described with respect to FIG. 1A for brevity. The device 110may include a forward looking antenna 114 and a backward looking antenna116. The device 110 may differentiate between signals received from theforward looking antenna 114 and those received from the backward lookingantenna 116 to determine information associated with the location ofdetected movement (e.g., whether the movement occurs in front of orbehind the device).

The signal may penetrate a wall 118 and be partially reflected by arunning individual 115, a sitting individual 120, a spinning ceiling fan125, and a stationary chair 130 on the opposite side of the wall. Thesignal also is partially reflected by a nearby stationary chair 135 thatis on the same side of the wall 118 as the user 105. The signal 120Areflected by the sitting individual 120 exhibits a small frequency shiftdue to the breathing movement of the individual's chest cavity. Thesignal 115A reflected by the running individual 115 exhibits a largerfrequency shift than the partially reflected signal 120A from thesitting individual 120, with this frequency shift being due to the morepronounced movement of the body of the running individual 115. Thesignal 125A reflected by the spinning ceiling fan 125 exhibits afrequency shift that is characteristic of a repeated mechanicalmovement. The signals 130A and 135A that are reflected by the stationarychair 130 and the nearby stationary chair 135 exhibit no frequencyshift.

The stepped-frequency sensor device 110 receives and processes thefrequency and phase information from the partially-reflected signals115A, 120A, 125A, 130A, and 135A. The signals may be received using asingle antenna or using forward and backward looking antennas. In aninitial scan function, the handheld stepped-frequency sensor device 110calibrates against data associated with partially-reflected signals115A, 120A, 125A, 130A and 135A that exhibit no frequency shift 130A and135A or only a frequency shift due to mechanically repeated movement(e.g., the ceiling fan 125) and data associated with the nearby chair135 that is located behind the device 110. The processed data indicatesmovement reflective of both breathing and running. The handheldstepped-frequency sensor device 110 provides an indication that a personwho is breathing and not otherwise moving and a person who is runninghave been detected. In some implementations, the handheldstepped-frequency sensor device may provide the indications by lightingseparate lights or providing other types of visual indicators on thehandheld stepped-frequency sensor device.

Referring to FIG. 1B, a device 150, such as a handheld stepped-frequencyradar scanner, includes antennas 155 and 160 for transmitting andreceiving a stepped-frequency radio frequency signal (an “RF signal”) todetect moving entities. The device 150 is shown as a bistatic radarsystem, in that there are separate antennas for transmitting andreceiving the RF signal. In particular, the antenna 155 is connected toa radar transmitter and transmits an RF signal toward a target, and theantenna 160 is connected to a radar receiver and receives a portion ofthe RF signal that is reflected by the target. In anotherimplementation, device 150 may be a monostatic radar system that uses asingle antenna to transmit and receive the RF signal. The followingdiscussion assumes that the antenna 155 is the transmitting antenna andthe antenna 160 is the receiving antenna.

The transmit antenna 155 is connected to a radar transmitter 165 thattransmits an RF signal toward a target. The RF signal includesfrequencies that cover a bandwidth in increments of frequency steps. Forexample, the signal may include a nominal frequency operating with acenter frequency in the UHF, L, S or X bands.

The receive antenna 160 is connected to a radar receiver 170 andreceives the reflected RF signal from the target. The receiver 170 iscoupled to a signal processing system 175 that processes received RFsignals from the receiving antenna 160. The signal processing system 175is coupled to a display 180 and a timing and control module 185. Thedisplay 180 provides an audible and/or a visual alert when an object isdetected by the scanner. The timing and control module 185 may beconnected to the transmitter 165, the receiver 170, the signal processor175, and the display 180. The timing and control module providessignals, such as a clock signal and control signals, to the othercomponents of the device 150.

Implementations may employ detection processes for slow or fast movementthat run in real-time on an embedded processor. Implementations also mayemploy interference detection processes.

FIG. 2A illustrates an antenna design 200 employed in one implementationof the device of FIG. 1B. The design 200 employs separate transmit 205and receive 210 antennas to simplify the electronics, provide spatialseparation and reduce very shallow reflections. The antennas 205 and210, which may serve as particular implementations of the antennas 105and 107 of FIG. 1B, may be placed in a housing 215, and a cover 220 maybe placed over the antennas. The cover 220 may be made of a suitableradome material.

FIG. 2B further illustrates aspects of the antenna design 200 discussedabove with respect to FIG. 2A. Although the following discussion refersto receive antenna 210, it is equally applicable to transmit antenna 205or other antennas. As shown, the design 200 employs a spiral antenna 210that permits significant size reduction. For an antenna to be anefficient radiator, it must normally have a dimension of at leastone-half wavelength. The spiral radiates efficiently when it has anouter circumference of at least one wavelength. This means that theantenna needs a maximum diameter of about one-third wavelength. Theupper frequency limit for efficient spiral radiation is set by the sizeof the feed point attachments, and the lower frequency limit is set bythe outer diameter of the spiral structure. Within these limits, thespiral radiates efficiently in a frequency-independent manner. The inputimpedance and the radiation patterns will vary little over thisfrequency range. The spiral antenna 210 may be constructed by etching aspiral pattern on a printed circuit board. A planar, printed circuit,spiral antenna radiates perpendicularly to the plane of the spiral. Thespiral 225 itself is located at the end of a cylindrical metal cavity230 (the cavity back) to provide isolation from neighboring elements andelectronics. Typically, an absorber 235 is used on the top side of thespiral inside the cavity 230 to make sure the element responds onlydownward.

The previous description provides an exemplary implementation of anantenna design. Other implementations may include different antennas,such as an endfire waveguide antenna. Such a configuration may beslightly larger than the spiral configuration. The endfire waveguideantenna reduces the measurement spot size, thus making the exactposition of the concealed object detected easier to locate. Othersuitable types of wideband antennas may also be used.

Referring to FIG. 3, a conversion system 300 includes a signal generator310, a signal control 320, a transmission switch 330, a receive switch340, and a mixer 350, which may be in the form of a quadraturedemodulator. In the system 300, a transmission signal is generated andtransmitted through a transmission antenna. Reflected portions of thetransmitted signal are received through a receive antenna, which mayoptionally be the same antenna as the transmission antenna. The antennasignal and the generated signal are input to the mixer 350, whichoutputs an in-phase signal and an out-of-phase (quadrature) signal. Thesignal generator 310 generates a signal to be broadcast by the antenna.The signal generator 310 may include a phase lock loop synchronized byan oscillator. In one implementation, a temperature controlled crystaloscillator is used to synchronize a voltage controlled oscillator. Thesignal generated by the signal generator 310 may be input to a mixer 350and to a signal control 320. The signal control 320 may amplify orotherwise conditions the signal to enable transmission by thetransmission antenna. The signal control 320 inputs the signal to thetransmission antenna and to a transmission switch 330. The transmissionswitch 330 enables feedback of the transmission signal to the mixer 350.The transmission switch 330 may include, for example, a single poledouble throw (SPDT) switch.

The transmission antenna emits the controlled signal and strikes objectsin the environment. Portions of the transmitted signal may be reflected.The reflected portions, which may exhibit a frequency and phase shift,are received by the receive antenna. The receive antenna inputs thereceived signal to a receive switch 340 that enables connection of thesignal to the mixer 350. The receive switch 340 may include, forexample, a SPDT switch.

Some implementations may use other mechanisms, such as a control system,in place of the transmission switch 330 and the receive switch 340. Inone implementation, the receive antenna is input directly to a mixerwithout a switch.

The mixer 350 receives the signal from the signal generator 310 in aninput. In another input, either the transmission signal or the receivedsignal is received by the mixer 350, based the transmission switch 330and the receive switch 340. The mixer 350 converts input signals to aform that is more easily processed, such as, for example, an in-phaseand an out of phase component at a baseband frequency.

As shown, the mixer 350 is a quadrature demodulator, though other signalconversion systems may be used. The quadrature demodulator outputs “I”and “Q” data (referred to as IQ data). The output signals may beprocessed, as discussed with respect to FIGS. 5 and 6, to determine thefrequency and phase shifts between transmitted and received signals thatmay be indicative of movement at a distance. In some implementations,separate IQ data may be generated for each transmitted frequency.

The previous description is an example implementation of the transmitand receive system. Other implementations may include differentcomponents. For example, in various implementations, a backward lookingantenna may be included to help eliminate signal clutter. Signals fromthe backward looking antenna may also be converted to IQ data andprocessed.

FIG. 4 shows a process 400 to detect moving entities. The process 400may be implemented on the system 150 of FIG. 1B or another system. Theprocess 400 begins when a stepped-frequency signal is transmitted by astepped-frequency sensor device (step 410). The stepped-frequency radarsignal may be a radar signal including multiple frequencies and phasesthat are transmitted concurrently or consecutively. In oneimplementation, each transmission includes a frequency bandwidth thatincludes multiple transmitted frequencies that are separated byfrequency steps. While cycling through the bandwidth, each frequency istransmitted for a period of time, followed by the next frequency, untilthe bandwidth has been crossed. Although multiple frequencies may besent, one after another, the transmitted and received signals arediscussed as a single signal to simplify discussion. After transmission,the signal strikes an object and is partially reflected.

The stepped-frequency sensor device detects the reflected portion of thesignal (step 420). This may be accomplished, for example, by using atransceiver, a separate antenna, or multiple separate antennas (e.g., aforward looking and backward looking antennas). The detected signalincludes a frequency that may have been altered by movement of thestruck object and a phase that may be affected by the distance to theobject.

The stepped-frequency sensor device processes the reflected portions ofthe signal (step 430). The processing, for example, may identifyinformation associated with frequency and phase shifts that may beindicative of the presence of moving objects or entities at a distance.The processing may include a calibration step to calibrate the data orprocessing steps based on conditions detected for a particular use ofthe device. Calibration may include removing or altering parts of thesignal indicative of clutter, repeated mechanical movement, orreflections near or behind the device. Processing may also includecalibration of the analysis steps, such as integration time.

The stepped-frequency sensor device analyzes the data to determine ifthe reflected portions of the signal are associated with moving objectsor entities (step 440). This may include, for example, Fouriertransforms for multiple integration times. The process 400 is an exampleimplementation of a process to sense moving entities using astepped-frequency sensor device. Some implementations may includeadditional or alternative steps. For example, processing and analyzingthe data (steps 430 and 440) may be conducted in a single step.

Referring to FIG. 5, a process 500 to detect moving entities may beimplemented on the system 100 of FIG. 1B or another system. In theprocess 500, multiple signal processing techniques may be employed. Inone implementation, the user may, at the time of use, determine whichprocess method or methods to employ. In other implementations, thedevice may be configured to determine the processing method or methodsto employ, for example, based on data calibration.

The stepped-frequency sensor device transmits a stepped-frequency signal(step 510) and detects the reflected portion of the signal (step 520).This may be accomplished, for example, as described previously withrespect to steps 410 and 420 of FIG. 4. Additionally or alternatively,detecting the reflected portion of the signal (step 520) may includeconverting the reflected portion of the signal to a usable form, suchas, for example, down-converting the signal to a baseband frequencyand/or converting the signal with an analog-to-digital converter.

The stepped-frequency sensor device calibrates data associated with thereflected portions of the signal (step 530). Calibration may includeremoving or altering data associated with parts of the signal indicativeof clutter, repeated mechanical movement, or reflection near or behindthe device. Calibrating the signal may also include determining whichprocessing method or methods, among multiple possible processingmethods, are appropriate, given the signal contents. For example, if thedata is indicative of too much or too little reflected signal beingreceived, the calibration step may enable a degraded signal process(step 540). Also, calibration may be used to tweak processing methods.For example, integration times may be increased or decreased tofacilitate processing and analysis.

A degraded signal process (step 540) processes the data to determinereliability of the results produced. The degraded signal process (step540) monitors for data that is, for example, indicative of situationsincluding detection of A/D converter saturations or unusually highsignal levels that may arise from the transmitted signal reflecting offmetal objects buried within or behind walls, detection of significantincreases in the noise floor resulting from intentional or unintentionaljamming, or detection of significant signal energy across all rangecells associated with excessive movement of the antenna. The processeddata is analyzed (step 545) to determine if an alert or indication isneeded to communicate to the user that the signal is degraded.

A subtle movement process (step 550) includes processing specialized todetect smaller movement. The subtle movement process (step 550) may beoptimized for detection of stationary personnel whose only significantmovement is that caused by respiration. The subtle movement process(step 550) may, for example, employ a longer integration time or ahigher Doppler resolution. The processed data is analyzed (step 555) todetermine if an alert or indication is needed to communicate to the userthat subtle movement has been detected.

An overt movement process (step 560) includes processing optimized todetect rapid movement. The overt movement process (step 560) isoptimized for detection of walking or moving personal. For example, eachtransmit frequency may be processed by a separate filter to enabledetection of short duration movements from the arms and legs ofstationary personnel as well as the detection of the main body movement,such as walking and running. The processed data is analyzed (step 565)to determine if an alert or indication is needed to communicate to theuser that rapid movement is detected.

The process 500 is an example implementation of a process to sensemoving entities using a stepped-frequency sensor device. Otherimplementations may include additional or alternative steps. Forexample, each of the subtle movement processing (step 550) and the overtmovement processing (step 560) may include a feature that determineswhether degraded signal processing (step 540) should be employed.

FIGS. 6-9B, and the discussion below, refer to a set of specificimplementations of the device. The specific implementations are referredto as wall penetrating personal detection sensors (WPPDS) and areprovided as one possible set of implementations of a sensor fordetecting moving entities.

In one implementation, a WPPDS employs a through-wall-detection radarsystem to detect personnel. The system includes a light-weight (e.g.,less than 1.5 pounds), portable, dedicated through wall system fordetection through non-metallic walls. Particular implementations of theWPPDS are configured to detect both moving and stationary (breathing)personnel. In the case of locating an individual buried under structuraldebris, distance and angle to the individual, which may be critical tothe life saving operation, are provided. In the case of hostagesituations, the WPPDS may be used to determine the position ofindividuals from certain locations, which may dictate the rescueoperation methodology.

A particular implementation employs an AN/PSS-14 mine detection radarsystem in a miniaturized 1.4 pound WPPDS unit that fits into asemi-automatic weapon (SAW) ammo pouch, and may operate for 180twenty-second cycles and otherwise remain on standby during a 16 hourperiod running on eight disposable AA batteries. The WPPDS detectsmoving targets through non-metallic wall materials (e.g., cement blocks,reinforced concrete, adobe, wallboard and plywood).

The WPPDS may employ coherent, stepped-frequency continuous wave (SFCW)radar that provides excellent through wall detection performance.Detection is realized through range-Doppler processing and filtering toisolate human motion.

In various implementations, data from a SFCW radar may be processed asan ensemble of fixed-frequency CW radars, allowing for the optimumdetection of the Doppler shift of a moving target over time via spectralanalysis. The stepped-frequency radar data may also be processed tocompress the bandwidth and obtain a high range resolution profile of thetarget. For example, the data may be processed to remove stationary orfixed time delay data, leaving the moving target data, to be evaluatedin both the range and Doppler (velocity) dimensions. A coherentfrequency-stepped radar may have an advantageous signal gain whencomputing the range and Doppler values of moving targets. Pulse type orfrequency chirp type radars may not be able to achieve the sameintegrated signal gain as stepped-frequency radar, due to a non-coherentnature.

Another property of a SFCW radar is the ability to operate inenvironments that exhibit high radio frequency interference (RFI). Shortpulse and frequency chirp radar systems maintain a wider instantaneousreceive bandwidth, enabling more RFI into a processing electronics chainand reducing the signal to noise/interference level, which may reducessensitivity and may degrades detection performance.

In one implementation, the SFCW radar system enables detection of subtleand overt movement through non-metallic walls. The SFCW radar systemuses processes that operate on hardware that is generally commerciallyavailable. The architecture of the SFCW radar system generally is lesssusceptible to jamming (intentional or unintentional) than other radararchitectures. Additionally, the reduced bandwidth enablesimplementation of more highly integrated RF technology, resulting in areduction in system size, weight and DC power.

With respect to the antenna, the antenna elements are miniaturized(scaled) versions of the AN/PSS-14 cavity-backed spiral design. Theminiaturized tactical antenna supports the selected frequency range (theupper end of the AN/PSS-14 operating range, which improves performanceagainst rebar) and packaging constraints.

The RF Electronics generate the frequency-stepped radar waveform,amplify the signal for transmission, receive energy reflected offtargets using a low-noise front end, and generate coherent (in-phase andquadrature, or I & Q) signals used in the detection process. Thetransceiver electronics feature a reduced bandwidth, which enables asingle VCO implementation compared to a more complex two VCO design.Further system miniaturization is achieved through implementation of adirect down-conversion (homodyne) receiver. A brassboard homodynereceiver has shown that significantly increased detection range inthrough wall applications is achievable compared to the phase-noiselimited AN/PSS-14 super-heterodyne architecture. The reduced bandwidthof the single-board TX/RX provides sufficient range resolutioncapability to support detection, and it avoids the NTIA/FCC restrictionsassociated with ultra wideband (UWB) radars. The transmit power, coupledwith the gain of the antenna, results in a low radiated power(approximately the same as cell phones), making the system safe forhuman exposure.

The digital signal processor (DSP) hosts the motion detection algorithmsThe WPPDS signal processing algorithm incorporates coherent integrationgain and robust detection algorithms, achieving superior performancewith greater detection range, higher probability of detection (Pd), andlower probability of false alarm (Pfa). Particular implementations maybe used to scan through damp concrete blocks and rebar, so as to permitready detection of moving personnel.

The system also include power supply circuitry needed to convert 6Vbattery power for the electronics. Bottoms-up power consumptioncalculations show that a set of disposable AA alkaline batteries mayprovide 180 twenty-second operating cycles.

The low power, compact, high-performance direct-conversion radartransceiver is realized through use of state of the art RF MMICs and theRF integrated circuits available. An ultra-low phase noise TCXO housedin a miniature surface-mountable package is used as a reference to asynthesizer chip with a VCO integrated on the chip. Loop response timeand phase noise are achieved and optimized via an external loop filter,creating a stable, fast-locking signal source with low divider noise.

The signal source is then amplified by high-efficiency monolithicamplifiers with integrated active biasing circuitry and on-wafer DCblocking capacitors. This approach minimizes part count and currentconsumption. This low-noise VCO is also used in the demodulation of thereceived radar return, which provides considerable phase noisecancellation due the oscillator coherency. With much lower phase noiseriding on returned signals (including near-wall reflections), thereceiver sensitivity is predominantly limited by thermal noise, enablingincreased detection range compared to the AN/PSS-14 radar receiver. Thisalso enables an increase in transmit power for increased range.

The direct-conversion quadrature demodulator includes polyphase filtersand ensures quadrature accuracy across the entire bandwidth.Pre-amplification of the LO and integrated variable gain control of thedemodulated signal allow for efficient use of circuit board real estateand provide the system with signal conditioning flexibility to maximizesignal dynamic range at the ADC inputs.

The DSP is used to process IQ data from the radar transceiver todetermine if objects are in motion and, if so, to alert the user. TheDSP has many features for power management, including dynamic frequencycontrol, dynamic core voltage control, and the capability of turning offunused sections of the IC. These power management features make this DSPan excellent choice for battery operated WPPDSs. Operating the WPPDS athalf the frequency and a core voltage of 1V allows us to lower the powerand also provides us with a programmable performance upgrade for thefuture. A clock frequency is provided by the RF transceiver board via anLVDS differential clock driver. This helps protect signal integrity andreduces EMI caused by the fast clock edge rates.

The design features 8M bytes of SDRAM for fast program access and enoughstorage for 60 seconds of captured data per operating cycle. Inaddition, 4M bytes of FLASH memory are used for booting up the DSP andfor non-volatile storage. A USB interface is used as a test port, andwill only be powered up for debugging and data collection. An analog todigital converter (ADC) includes an 18 bit ADC, that allows a 15 dBincrease in SNR to take advantage of the increased dynamic range andsensitivity. Differential inputs improve common-mode noise cancellation,allowing for a more sensitive detector. The op-amps are selected for lowpower, low noise performance as amplifiers and active filters A 16 bitDAC is used to cancel the DC offset from the incoming IQ signals fromthe RF Electronics. SPI serial communication protocol is used tocommunicate with the ADCs, DAC, and RF PLL, which helps reduce I/Orequirements and EMI.

Referring to FIG. 6, data may be processed according to process 600 thatmay be implemented on the system 100 of FIG. 1B. The process 600receives IQ data that may be generated, for example, as discussed withrespect to FIG. 3. The process 600 involves multiple signal processingsteps, including degraded performance processing 610, overt movementprocessing 625, and subtle movement processing 675. For simplicity, thetypes of signal processing are discussed separately, though thedifferent types of processing may be concurrently carried out on thesame input signals. Each processing type may be associated with aspecific alert generation function 665. In various implementations, inboth overt movement processing 625 and subtle movement processing 675,phase and/or frequency data for each transmitted frequency is first usedto develop a current picture of an environment, and is then comparedagainst further phase and frequency data to determine differences.

The processing method incorporates coherent integration gain and robustdetection algorithms, achieving superior performance with greaterdetection range, higher probability of detection (Pd), and lowerprobability of false alarm (Pfa). The process 600 begins when IQ data isinput to be processed 605. In one implementation, the user inputs one ormore commands associated with either overt moving processing 625, subtlemovement processing 675, or both. In various implementations, a singlecommand may be pressed, which may, depending on the reflected signal,trigger overt moving processing 625, subtle movement processing 675, orboth. IQ data is input to a calibration function 635 and to a saturationdetection function 615. The saturation detection function 615 sends datato a degraded performance detection 620 function, which monitors forsituations including detection of A/D converter saturations or unusuallyhigh signal levels that may arise from the transmitted signal reflectingoff metal objects buried within or behind walls, detection ofsignificant increases in the noise floor resulting from intentional orunintentional jamming, and detection of significant signal energy acrossall range cells associated with excessive movement of the antenna. Thedata from the degraded performance detection 620 is sent to the alertgeneration function 665, which may trigger an alert to specify thedetection of a degraded signal. The alert may signify to the user thatprocessing results may be less reliable. Degraded performance processing610 need not interrupt other processing.

In overt movement processing 625, the IQ data may first be sent througha calibration function 635 to minimize the effects of non-idealtransceiver hardware. Calibration provides compensation for DC offseterrors, IQ gain and phase imbalance, and gain and phase fluctuationacross frequency. Target detection performance may be improved as aresult of cleaner range and Doppler profiles. Hardware support for thisfunction includes solid state RF switches in the receive and transmitantenna front end(s) that enable the receiver input to be switched fromthe antenna to either resistive load or to a reduced power sample of thetransmit signal. Calibrated data may be used in overt movementprocessing 625 and subtle movement processing 675.

Overt movement processing 625 is optimized for rapid detection of movingpersonnel. Processing delays associated with filtering and coherentintegration are short, providing an alert of detectable movement withinone second of the event. The overt movement processing 625 begins withthe data output from the calibration function 635 input to the movingtarget indication (MTI) filter 690 to eliminate strong returns fromstationary clutter, or returns from objects within a proximity from theWPPDS (e.g., objects on the same side of a wall as the WPPDS). Eachtransmit frequency may be processed by a separate filter having abandpass response that passes signals from separate target velocities.Separate filters may enable detection of short duration movements fromthe arms and legs of stationary personnel as well as the detection ofthe main body movement, such as walking and running.

The data output from the MTI filter 640 is input to the high rangeresolution (HRR) process 640. In one implementation, the HRR process 640uses an inverse fast fourier transform (IFFT) to transform the ensembleof returns from the received signal to HRR profiles. In otherimplementations, other transforms may be used. Depending on thecharacteristics of the results, the HRR process 640 results may be inputto the degraded performance detection 620 as well as Doppler processing650.

Doppler processing 650 may provide additional coherent integration gainto further improve the signal-to-noise ratio. A region detection 655function then selects a Doppler bin with amplitude regions from rangeresolution cells. The region amplitudes are passed on to a Rangeconstant false alarm rate (CFAR) function 660.

The Range CFAR function 660 is a cell-averaging constant false alarmrate (CA-CFAR) detector and operates along the HRR range cells outputfrom the region detector 655. The range cells are compared to thesurrounding cells. A detection may be sent to the alert generation 665if calculated parameters of the cell under test are greater than apredetermined amount.

The alert generation 665 function may perform additional clean-up of thedetection map, including, for example, removal of detections beyond arange, and encoding the detection as either near or far.

Subtle movement processing 675 is optimized for detection of stationarypersonnel whose only significant movement is that caused by respiration.Subtle movement processing 615 includes the calibration function 635,the HRR process 645 and the Doppler processing 650, but with longerintegration times. A longer integration time provides fractional-hertzDoppler resolution to resolve the carrier modulation sidebandsassociated with breathing. The HRR process 645 is performed directly onthe calibrated radar data, bypassing the MTI filters that may otherwiseremove the respiration sidebands

In subtle movement processing 675, the output of the Doppler processing650 is sent to a Doppler CFAR function 680. The Doppler CFAR function680 may be applied across the Doppler processing 650 output to identifyportions of the spectrum that are significantly above the noise floor.Values selected by the Doppler CFAR function 680 may be input to thespectrum variance estimation 685 function where the power-weightedsecond-moment of the spectrum is determined. If the calculated spectrumvariance 685 is within limits typical of respiration, the alertgeneration function 665 may declare detection of subtle movement.

Referring to FIGS. 7A and 7B, the compact WPPDS package enablessingle-handed operation while providing robust protection for theintended application. The unit may also be attached to the forearm orupper arm via straps. As shown in FIG. 7A, the unit fits in a SAW ammopouch. The housing layout is able to be configured with three circuitcard assemblies (CCA), which enables an optional integrated batteryrecharging circuit, such as a generally commercially availableintegrated battery recharging circuit. The miniature cavity-backedspiral antennas each contain a planar feed assembly that connectsdirectly to the RF CCA. The Digital CCA contains the DSP as well as thepower supply (PS) circuitry.

As shown in FIG. 7B the WPPDS unit and accessories fits into a standardPelican case for storage and transportation. The packaging providesprotection against transportation shock and vibration, environmentalprotection, and facilitates safe storage and ease of handling while indaily use by soldiers or rescuers. The case includes compartments forstoring arm straps, extra batteries, and an optional vehicle-compatibleAA battery recharger.

To deploy, the operator may hold the system by the straps or by thesides of the unit, affix the unit to either arm via the straps (forearmor upper arm), or mount the system to a pole or tripod (pole/tripod notprovided with unit). A standard video camera mount may be connected tothe bottom of the unit to facilitate mounting to a tripod or pole. Thehousing design also features raised stiffener ridges on the front thatmay facilitate temporary wall mounting using putty.

The housing is made of impact-resistant ABS plastic to help provideprotection if the case is dropped or collides with hard objects that mayoccur during training exercises or during operation, such as on abattlefield or in a rescue operation. The external design of the housingincorporates human factors features to simplify operation in difficultenvironments. The light emitting diodes (LEDs) are recessed to provideshadowing to enhance daytime vision, as illustrated in FIG. 9A. A rubbershield protects the front of the unit. Rubber grip pads are alsoprovided in four areas to facilitate slip-free handheld operation.Multiple SCAN switches support a variety of operational situations.

For operational simplicity, WPPDS is designed to operate while poweredby AA batteries, as shown in FIG. 8A. The PS connects to the batteryholder assembly, which features all eight batteries in the sameorientation for easy installation under low light/time criticalconditions. The total power draw from AA batteries is estimated to be2.2W. Four batteries are connected in series, and 2 sets of 4 batteriesin parallel. This provides 6V and divides the power by the 2 batterysets. During run time the individual battery voltage is allowed to decayfrom 1.4V to 0.9V, providing approximately 1 hour of operation time, asshown in FIG. 8B.

As shown in FIG. 9A, a simple operator interface provides features tosupport required operational capability.

Referring to FIG. 9B, power ON/OFF is controlled via OFF and STDBYswitches. In Standby mode the circuitry is placed in a power-save mode,and activation of any one of three SCAN pressure switches (one front,two bottom) initiates immediate sensor operation. The system returns tostandby mode when the SCAN button is released. Other implementations mayinclude other interface arrangements. For example, a combination of twoSCAN switches could be simultaneously pressed (but not held) to enabletimed operation, such as when the unit is temporarily adhered to orleaned against a wall, or mounted to a tripod, for hands-off operation.

Four color LEDs provide indications to the operator. The yellow STANDBYLED indicates power status: steady illumination indicates power is on;flashing LED indicates low battery power. The red FAULT LED indicatesone of several conditions: steady illumination indicates that the systemis unable to make an accurate measurement due to metal blockage,electromagnetic interference, or excessive motion of the sensor;flashing illumination indicates a built-in-test (BIT) failure. The greenSCANNING LED remains illuminated while the unit is operating to detectmotion. The blue DETECT LED indicates that motion has been detected.Steady illumination indicates personnel motion detection at a closerdistance. A flashing DETECT LED indicates personnel motion detection ata farther distance. A change in color for the blue DETECT (to Magenta)indicates that subtle movement has been detected.

The system may be powered on and placed in standby mode by momentarilypressing the STDBY switch. The unit may be powered off by simultaneouslypressing the STDBY and OFF switches. This may prevent accidentalpower-down during normal operation should the OFF switch getaccidentally bumped. In STDBY mode, circuitry is activated in power-savemode, and the unit may be immediately operated by pressing one of theSCAN switches. The front SCAN switch may be activated by pressing andholding the WPPDS unit against the wall to be penetrated. One of twobottom SCAN switches may be activated by squeezing with the thumb(normal unit orientation) or index finger (inverted orientation), or bypressing the unit against the knee or thigh when in a kneeling position.

When any SCAN switch is depressed, the green SCAN LED may illuminate,and may remain illuminated as long as the SCAN switch is depressed. Thismay alert the operator that the unit is operational (i.e., that the SCANswitch is properly depressed). A blue DETECT LED may be used to alertthe operator of detected personnel.

The unit may also be programmed to detect subtle movement. This mode maybe initiated by pressing any SCAN switch twice in rapid succession. Thegreen SCAN LED may pulsate slowly when this mode is active (similar to alaptop's power LED in standby mode). The blue DETECT LED may illuminatewhen slow movement (respiration) is detected.

Because the antennas have conical radiation patterns, the unit may bearbitrarily oriented (within the plane of the wall); i.e., when heldagainst the wall, the unit may be oriented horizontally, vertically, orin any other position without impacting operational performance. Theunit may also be held off the wall (standoff), provided it is held stillduring SCAN operation.

Although the techniques and concepts have generally been described inthe context of a handheld stepped-frequency scanner, otherimplementations are contemplated, such as a vehicle-mountedstepped-frequency scanner.

Other implementations are within the scope of the following claims.

1. A method of sensing moving entities, the method comprising:transmitting a stepped-frequency radar signal including a plurality offrequencies, at least a portion of the transmitted radar signal movingthrough a wall from a first side of the wall to a second side of thewall; receiving reflected portions of the radar signal with a firstantenna arranged to receive reflected radar signals at a first locationand a second antenna arranged to receive reflected radar signals at asecond location; processing the reflected portions received from thefirst and second antennas to generate processed data includinginformation associated with frequency shifts between the transmittedsignal and the reflected portions of the radar signal received at thefirst location and information associated with frequency shifts betweenthe transmitted signal and the reflected portions of the radar signalreceived at the second location; and analyzing the processed data todetermine if reflected portions of the radar signal are associated withmoving entities located beyond the second side of the wall.
 2. Themethod of claim 1, wherein analyzing the processed data includescalibrating the processed data.
 3. The method of claim 2, whereincalibrating the processed data includes compensating for reflectionsnear the first or second antennas.
 4. The method of claim 2, whereincalibrating the processed data includes compensating for reflectionsbehind the first or second antennas.
 5. The method of claim 2, whereinthe processed data is calibrated for each separate attempt to sensemoving entities.
 6. The method of claim 1, wherein analyzing theprocessed data includes removing information associated with reflectionsfrom stationary objects.
 7. The method of claim 1, wherein analyzing theprocessed data includes removing information associated with reflectionsfrom objects within a proximity to the first or second antennas.
 8. Themethod of claim 1, wherein analyzing the processed data includesperforming a Fourier transform on information associated with theprocessed data, the method further comprising detecting degradedperformance based on whether results of the Fourier transform meet acharacteristic.
 9. The method of claim 1, wherein analyzing theprocessed data includes performing a first Fourier transform with afirst integration time and a second Fourier transform with a secondintegration time longer than the first integration time on the sameinformation associated with the processed data.
 10. The method of claim9, further comprising detecting degraded performance based on whetherresults of the first Fourier transform meet a first characteristic andresults of the second Fourier transform meet a second characteristicdifferent from the first characteristic.
 11. The method of claim 1,wherein analyzing the processed data includes analyzing frequency andphase shifts between the transmitted signal and the detected signal todetermine movement of objects at a distance.
 12. The method of claim 1wherein the transmitting, receiving and processing is performed by aportable device.
 13. The method of claim 1 wherein the portable devicecomprises a handheld device.
 14. The method of claim 1 wherein receivingreflected portions of the radar signal with the first antenna and thesecond antenna includes receiving reflected portions of the radar signalwith a first antenna located on a first half of a device and a secondantenna located on a second half of the device, where the first half ofthe device is closer to the first side of the wall than the second halfof the device.
 15. The method of claim 1 wherein receiving reflectedportions of the radar signal with the first antenna and the secondantenna includes receiving reflected portions of the radar signal with afirst antenna located on a half of a device and a second antenna locatedon the other half of the device.
 16. A system for sensing movingentities, the system comprising: a stepped-frequency radar transmitterconfigured to transmit a stepped-frequency radar signal; a first antennaarranged to receive reflected radar signals at a first location; asecond antenna arranged to receive reflected radar signals at a secondlocation; and a processor configured to: process the reflected portionsreceived from the first and second antennas to generate processed dataincluding information associated with frequency shifts between thetransmitted signal and the reflected portions of the radar signalreceived at the first location and information associated with frequencyshifts between the transmitted signal and the reflected portions of theradar signal received at the second location, and analyze the processeddata to determine if reflected portions of the radar signal areassociated with moving entities located beyond a far side of a wall. 17.The system of claim 16 further comprising a demodulator which receivesboth the stepped-frequency radar signal and a reflected portion of theradar signal, wherein the demodulator outputs in phase and out of phasedata.
 18. The system of claim 16, wherein the system is configured to beoperable using AA batteries.
 19. The system of claim 16, wherein theprocessor is configured to remove information associated with signalreflection from stationary objects.
 20. The system of claim 16, whereinthe processor is configured to remove information associated withsignals reflected from objects within a proximity to the first or secondantennas.
 21. The system of claim 16, wherein the processor isconfigured to perform a first Fourier transform with a first integrationtime and a second Fourier transform with a second integration timelonger than the first integration time on the same informationassociated with the processed data.
 22. The system of claim 16, whereinthe processor is configured to calibrate or process reflected portionsof the radar signal based on which of the first and second antennasreceives the reflected portion of the radar signal.
 23. The system ofclaim 16 wherein the system comprises a portable device.
 24. The systemof claim 23 wherein the portable device comprises a handheld device. 25.The system of claim 16 wherein the first antenna is located on a firsthalf of a device and a second antenna is located on a second half of thedevice, where the first half of the device is closer to the first sideof the wall than the second half of the device.
 26. The system of claim16 wherein the first antenna is located on a half of a device and asecond antenna is located on the other half of the device.